Root cause analysis is a class of problem solving methods aimed at identifying the root cause(s) of a problem or event in order to create effective corrective actions that will prevent that problem or event from recurring.
Root cause analyses have successfully been used in numerous machine failure investigations.
Findings from root cause analyses can be utilized to redesign a machine improving working conditions for a failing component. Findings from root cause analyses can further be used to monitor and control root-cause parameters, such as load, temperature, electrical stray currents, lubrication failures and hydrogen diffusion flux. Redesign, monitoring and control can be used to avoid or at least reduce the risk for premature failures.
In premature failure of machines the root cause analyses involves load and strength for the failing component. This analyses start with an analysis of the machine operating conditions, the external loads, internal machine resonances, loads and operational conditions all the way down to tribology contact conditions and the detailed stress fields in the component.
The complexity of the machine systems, the large number of interacting components, uncertainties in process loads, environmental and running conditions make the stress analyses in the components difficult. The uncertainty in stress analyses depends on the static and dynamic conditions of the load. Turbo machinery such as wind mills, marine pods, pumps and fans may have running conditions for which it is difficult to estimate the real loads. Uncertainties in stress analyses are further linked to the constraints and simplifications that are often made in order speed up or even make simulations possible. Bearings in pliant structures may be poorly supported, changing the stress distributions in rings and rollers. Rolling elements may further be forced to move, skew and even partly jam causing higher stresses in reality than those derived in calculations.
Strength analysis involves investigations of components, such as bearings, gears, lubricants, houses or shafts. The conformance with specifications and tolerances are checked.
Signs for wear, smearing, galling, micropitting, spalling, plastic deformation, surface distress, cracks, wear patterns from loads contact and corrosion on the failed components are investigated. Near surface and subsurface material decay, changes in residual stress and x-ray line broadening, micro structural changes and fatigue development of components and aging of lubricants are also investigated. Signs of damage, wear, load or corrosion on adjoining components give additional information. Lack of damage on adjoining components may also provide knowledge on the machine's running conditions, its load and environmental conditions.
The failures are often detected at a late stage where initial failure mode is partly hidden behind secondary failures. Stresses, load cycles, temperature and material strength are compared to fatigue and fracture calculations. These findings are compared to the failure observations. When root cause failure analyses are non-conclusive there often remains an uncertainty in both load and stress estimates as well as in environmental weakening of the component.
Environmentally induced weakening or cracking can be found under a range of stress conditions. Cracks can be driven by embrittlement processes as well by anodic dissolution. Nasal or atomic hydrogen can sometimes be linked to environmental induced weakening and extensive crack propagation.
Environmental induced strength reduction is caused both by corrosion and tribocorosion processes.
Corrosive reactions are due to an irreversible oxidation-reduction reaction between a metal and an oxidizing agent present in the metal's environment. The oxidation of the metal is inseparably coupled to the reduction of the oxidizing agent, i.e.Metal+oxidizing agent→oxidized metal+reducing agent
The following reactions take place:Anode partial reaction Fe→Fe2++2e−Cathode partial reaction 2H++2e−−>H2 Overall reaction Fe+2H+→Fe2++H2 
In the cathode reaction hydrogen gas is formed by the recombination of two hydrogen atoms, which are separately formed on the cathode surface.H+e−→Hads 
This Volmer reaction produces an adsorbed hydrogen atom on the surface.
It is normally the rate limiting reaction. In a second step hydrogen atoms recombine into gas. Two processes are knownHads+H+->H2 Heyrovsky reactionHads+Hads->H2 Tafel reaction
Alternatively, the adsorbed hydrogen can also diffuse into the metal.Hads->Hm Hm Hydrogen dissolved in component,
Chemical compounds e.g. in the lubricant may reduce hydrogen recombination rates. The relation of Hm to H2 increases. The Hm content in the high strength steel matrix increases as does the risk for hydrogen embrittlement and/or increased crack growth rates. Hydrogen atoms are diffusing or trapped in reversible or irreversible traps. The nature of the trap, the temperature and the stress field determines whether a trap irreversible or reversible.
Atomic H can diffuse measurable distance into metal components. A steel plate with a thickness of 0.5 mm will be penetrated by H-diffusion within a couple of hours. Hydrogen may cause embrittlement and cracking of high strength components at a distance from its place of origin.
Humidity and water increase the risk for corrosion and tribocorrosion processes. The hydroscopity of water drives a significant amount of water in and out of lubricants. At stand still water content is increased, and during running operations the water content is reduced. Bearing life reduction of up to 100 times is seen in standstill corrosion tests.
Gear oils with high amounts of additives may for example release water (possibly including ionic compounds with polar components) during stand still. Water is surface active, and condensed or free water may be concentrated into crevasses, pits and narrow gaps between metal components, which may result in corrosion.
Tribocorrosion is a material degradation process due to the combined effect of corrosion and wear. Wear influences corrosion rates by removing passivating and corrosion protecting surface layers while corrosion changes friction, wear processes and wear rate. An additional feature of tribocorrosion in lubricated contacts is the exposure of the active metal surface to an electrolyte. Reactions with e.g. acids may form Hads. These increases further the risk for introducing atomic hydrogen Hm into the stressed components.
Root cause analysis may for example be used to reduce or eliminate the adverse effects of corrosion or tribocorrosion, which occurs in many engineering fields and which can significantly reduce the service life of machine components. Detection of nasal metal hydrogen will be an important tool in the root cause analyses. It may also be use monitor components and machines detecting environmental weakening of components and parts.